The plasma membranes of spermatozoa will be studied to obtain information about the surface chemistry and organization of membrane lipids and sialoglycoproteins during maturation of sperm in the epididymis and in the female tract during capacitation. Treatments which alter the chemistry and/or organization of either lipid or sialoglycoprotein constituents of plasma membranes will be tested for their ability to induce an acrosome reaction and to abolish the need for sperm capacitation prior to fertilization. The preimplantation stages of blastocyst attachment to uterine epithelium will be similarly studied to determine what membrane components are necessary for adhesion or attachment between uterine epithelium and blastocysts. Rabbit ova will be studied to characterize the surface materials coating the plasma membrane of the fertilized ovum. Replicas of spermatozoon, ovum and blastocyst surfaces will be made by means of freeze-cleavage or freeze-etching procedures in order to map the distribution of surface markers (ferric oxide hydrosols, cationized ferritin and lectins) bound selectively by plasma membrane glycoproteins or sialoglycoproteins. The distribution of these markers after certain treatments will serve as a basis for determining how alterations in membrane properties may be related to the reorganization of membrane components. Information obtained about the structure of spermatozoon, ovum and blastomere plasma membranes and the ability to alter the organization of their membrane constituents will contribute to an understanding of what membrane changes are involved in the acquisition of sperm competence to fertilize ova, in the inhibition of polyspermy and the regulation of blastocyst implantation.